Define $A @ B$ to be $\frac{A}{B}+A\times B$. What is the value of $20 @ (4 @ 2)$?
Explanation: Substitute 4 for $A$ and 2 for $B$ in the expression defining $A @ B$ to find that $4@2=\frac{4}{2}+4\cdot2=10$. Then substitute 20 for $A$ and 10 for $B$ to find that $20@10=\frac{20}{10}+20\times10=\boxed{202}$.